1. Field of the Invention
The present invention relates to a method for simulating a diode, and more specifically, to a method for simulating the diode by using SPICE (Simulation Program with Integrated Circuit Emphasis).
2. Description of the Related Art
Circuit simulation is performed in the design and manufacture of electronic circuits to determine if the electronic circuits would operate in the intended manner and to predict the circuits' performance. Among the simulation programs, SPICE is the most widely used general-purpose circuit simulation program. SPICE simulates, with input information of model data, device parameter data and design data, a circuit model by employing equations which attempt to define mathematically the operation of the various circuit components in the circuit design, and provides output signal information as a result of the simulation.
For simulating a diode with SPICE, electrical characteristics are measured from two diode structures having different areas and lengths and then device parameters of the diodes are extracted from the measured results. These values are normalized to obtain a SPICE model of the diode. By applying area and length variables of a diode to be simulated by the SPICE model, electrical characteristics of the diode can be predicted.
However, when the SPICE model is applied to any values of area and length variables, the predicted result may not be exact, because the diodes used in extracting the device parameters are structurally different from the simulated diodes in terms of the number of contacts to the diode, distance from the end of the contact, current flow, crowding effect and so on. Therefore the conventional SPICE model may fail to exactly reflect varying electrical characteristics of the structurally different diode.
FIGS. 5a–5d show voltage-current characteristic curves for illustrating the problem of the conventional simulation method. In FIGS. 5a–5d, the solid line represents simulated current curve while the dotted line depicts actually measured current curve. The I–V characteristic curve of FIG. 5a shows that the simulated curve approximately identical to the measured curve when diode structure having area of 18,750 μm2 and peripheral length of 550 μm is employed. However, the I–V characteristic curves of FIGS. 5b to 5d reveal that the simulated curves are deviated from the actually measured I–V characteristics when the SPICE model obtained from the conventional method is applied to the differently structured diodes having area of 7,875 μm2 and peripheral length of 43,876 μm, area of 8,500 μm2 and peripheral length of 34,000 μm, and area of 2,627.64 μm2 and peripheral length of 33,408 μm, respectively.